Huc-MSCs-derived exosomes attenuate neuropathic pain by inhibiting activation of the TLR2/MyD88/NF-κB signaling pathway in the spinal microglia by targeting Rsad2

BACKGROUND

Mesenchymal stem cells (MSCs)-derived exosomes have shown promise as a cell-free therapeutic strategy for neuropathic pain. This study was conducted to explore the potential mechanisms underlying the analgesic effects of MSC-derived exosomes in treating neuropathic pain.

METHODS

Human umbilical cord MSCs (huc-MSCs)-derived exosomes were isolated and identified. BV-2 microglia were stimulated with lipopolysaccharide (LPS) in the presence or absence of exosomes. Differentially expressed proteins were identified by tandem mass tag (TMT)-based proteomic analysis. The analgesic effects of huc-MSCs-derived exosomes were evaluated in a rat model of chronic constriction injury (CCI). The underlying mechanism was investigated by flow cytometry, RT-qPCR, Western blotting, immunofluorescent staining, and small interfering RNA transfection.

RESULTS

In vitro, huc-MSCs-derived exosomes suppressed LPS-induced microglial activation and inhibited activation of the TLR2/MyD88/NF-κB signaling pathway. Based on the proteomic analysis, Rsad2 was identified and confirmed to be down-regulated by huc-MSCs-derived exosomes. Importantly, knockdown of Rsad2 also inhibited microglial activation and restrained activation of the TLR2/MyD88/NF-κB signaling pathway. In vivo, intrathecal injection of exosomes ameliorated CCI-induced mechanical allodynia, down-regulated Rsad2 expression and restrained TLR2/MyD88/NF-κB signaling activation in the spinal microglia.

CONCLUSION

Huc-MSCs-derived exosomes exerted analgesic effects on neuropathic pain by inhibiting activation of the TLR2/MyD88/NF-κB signaling pathway in the spinal microglia. The mechanism underlying these antinociceptive effects involved exosome-mediated interference with Rsad2 expression, thereby inhibiting microglial activation.

Iron deficiency alters expression of dopamine-related genes in the ventral midbrain in mice

A clear link exists between iron deficiency (ID) and nigrostriatal dopamine malfunction. This link appears to play an important role in at least restless legs syndrome (RLS) if not several other neurological diseases. Yet, the underlying mechanisms remain unclear. The effects of ID on gene expression in the brain have not been studied extensively. Here, to better understand how exactly ID alters dopamine functioning, we investigated the effects of ID on gene expression in the brain, seeking to identify any potential transcription-based mechanisms. We used six strains of recombinant inbred mice (BXD type) known to differ in susceptibility to ID in the brain. Upon weaning, we subjected mice from each strain to either an iron-deficient or iron-adequate diet. After 100 days of dietary treatment, we measured the effects of ID on gene expression in the ventral midbrain, a region containing the substantia nigra. The substantia nigra is the base of the nigrostriatal dopamine pathway and a region particularly affected by iron loss in RLS. We screened for ID-induced changes in expression, including changes in that of both iron-regulating and dopamine-related genes. Results revealed a number of expression changes occurring in ID, with large strain-dependent differences in the genes involved and number of expression changes occurring. In terms of dopamine-related genes, results revealed ID-induced expression changes in three genes with direct ties to nigrostriatal dopamine functioning, two of which have never before been implicated in an iron-dopamine pathway. These were stromal cell-derived factor 1 (Cxcl12, or SDF-1), a ferritin regulator and potent dopamine neuromodulator, and hemoglobin, beta adult chain 1 (Hbb-b1), a gene recently shown to play a functional role in dopaminergic neurons. The extent of up-regulation of these genes varied by strain. This work not only demonstrates a wide genetic variation in the transcriptional response to ID in the brain, but also reveals two novel biochemical pathways by which iron may potentially alter dopamine function.